The United States Environmental Protection Agency (EPA) has promulgated rules governing the type of processes that can be used to treat wastewater sludge.
Under 40 CFR 257, a Process to Further Reduce Pathogens (PFRP) must be used where sewage sludge or septic tank pumping are to be applied to a land surface or are incorporated into the soil, and crops for direct human consumption are to be grown on such land within eighteen (18) months subsequent to application or incorporation.
A Process to Significantly Reduce Pathogens (PSRP) must be used where sewage sludge or septic tank pumping are to be applied to a land surface or incorporated into the soil and the public will have access to such land within twelve (12) months subsequent to application or incorporation, or grazing animals, whose products are consumed by humans, will have access to such land within one (1) month subsequent to application or incorporation.
Appendix II or 40 CFR 257 classifies the following as PSRP and PFRP processes: